Ion Beams in Multi-Species Plasma

Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas

Spatial Structure of Ion Beams in an Expanding Plasma

We report spatially resolved perpendicular and parallel, to the magnetic field, ion velocity distribution function (IVDF) measurements in an expanding argon helicon plasma. The parallel IVDFs, obtained through laser induced fluorescence (LIF), show an ion beam with v ≈ 8000 m/s flowing downstream and confined to the center of the discharge. The ion beam is measurable for tens of centimeters along the expansion axis before the LIF signal fades, likely a result of metastable quenching of the beam ions. The parallel ion beam velocity slows in agreement with expectations for the measured parallel electric field. The perpendicular IVDFs show an ion population with a radially outward flow that increases with distance from the plasma axis. Structures aligned to the expanding magnetic field appear in the DC electric field, the electron temperature, and the plasma density in the plasma plume. These measurements demonstrate that at least two-dimensional and perhaps fully three-dimensional models are needed to accurately describe the spontaneous acceleration of ion beams in expanding plasmas

Confocal Laser Induced Fluorescence with Comparable Spatial Localization to the Conventional Method

We present measurements of ion velocity distributions obtained by laser induced fluorescence (LIF) using a single viewport in an argon plasma. A patent pending design, which we refer to as the confocal fluorescence telescope, combines large objective lenses with a large central obscuration and a spatial filter to achieve high spatial localization along the laser injection direction. Models of the injection and collection optics of the two assemblies are used to provide a theoretical estimate of the spatial localization of the confocal arrangement, which is taken to be the full width at half maximum of the spatial optical response. The new design achieves approximately 1.4 mm localization at a focal length of 148.7 mm, improving on previously published designs by an order of magnitude and approaching the localization achieved by the conventional method. The confocal method, however, does so without requiring a pair of separated, perpendicular optical paths. The confocal technique therefore eases the two window access requirement of the conventional method, extending the application of LIF to experiments where conventional LIF measurements have been impossible or difficult, or where multiple viewports are scarce

Understanding electron heat flux signatures in the solar wind

Suprathermal electrons (E > 80 eV) carry heat flux away from the Sun. Processes controlling the heat flux are not well understood. To gain insight into these processes, we model heat flux as a linear dependence on two independent parameters: electron number flux and electron pitch angle anisotropy. Pitch angle anisotropy is further modeled as a linear dependence on two solar wind components: magnetic field strength and plasma density. These components show no correlation with number flux, reinforcing its independence from pitch angle anisotropy. Multiple linear regression applied to 2 years of Wind data shows good correspondence between modeled and observed heat flux and anisotropy. The results suggest that the interplay of solar wind parameters and electron number flux results in distinctive heat flux dropouts at heliospheric features like plasma sheets but that these parameters continuously modify heat flux. This is inconsistent with magnetic disconnection as the primary cause of heat flux dropouts. Analysis of fast and slow solar wind regimes separately shows that electron number flux and pitch angle anisotropy are equally correlated with heat flux in slow wind but that number flux is the dominant correlative in fast wind. Also, magnetic field strength correlates better with pitch angle anisotropy in slow wind than in fast wind. The energy dependence of the model fits suggests different scattering processes in fast and slow wind

The ion velocity distribution function in a current-free double layer

A portable, low-power, diode laser-based laser-induced fluorescence(LIF)diagnostic incorporating a heated iodine cell for absolute wavelength reference was installed on the Chi-Kung helicon source [K. K. Chi, T. E. Sheridan, and R. W. Boswell, Plasma Sources Sci. Technol.8, 421 (1999)] to measure the ion velocity distribution function of argon ions as they transited a current-free double layer (DL) created where the solenoidal magnetic field diverges at the junction of the plasma source and the diffusion chamber. Based on LIFmeasurements of the transiting ion beam energy, the strength of the potential drop across the DL increases with decreasing neutral pressure and increasing magnetic field strength in the source. The location of the double layer also moves further downstream of the helicon source with increasing pressure. LIFmeasurements of the ion beam energy were found to be in good agreement with measurements obtained with a retarding field energy analyzer and also with numerical predictions.This work was supported by NSF Grant PHY-0315356, and the NSF EAPSI program in cooperation with Australian Academy of Science. A.M.K. was also supported by the DOE Fusion Energy Science Fellowship program

Electron and proton heating by solar wind turbulence

Previous formulations of heating and transport associated with strong magnetohydrodynamic (MHD) turbulence are generalized to incorporate separate internal energy equations for electrons and protons. Electron heat conduction is included. Energy is supplied by turbulent heating that affects both electrons and protons, and is exchanged between them via collisions. Comparison to available Ulysses data shows that a reasonable accounting for the data is provided when (i) the energy exchange timescale is very long and (ii) the deposition of heat due to turbulence is divided, with 60% going to proton heating and 40% into electron heating. Heat conduction, determined here by an empirical fit, plays a major role in describing the electron data

First You Buy the Moisturizer, Then You Pay the Price: An Overview of the United States\u27 Lack of Cosmetic Market Regulations and How it Harms the Consumers

The article discusses the lack of regulation in the cosmetic industry in the U.S. and how it affects consumer\u27s health. It is reported that the absence of strict regulations has resulted in cosmetics that contain harmful ingredients, which pose risks to the health of consumers. It also examines the gendered marketing of cosmetics, which has contributed to the industry\u27s lack of regulation